Fitness minimization and dynamic instability as a consequence of predator-prey coevolution

Summary We analyse dynamic models of the coevolution of continuous traits that determine the capture rate of a prey species by a predator. The goal of the analysis is to determine conditions when the coevolutionary dynamics will be unstable and will generate population cycles. We use a simplified model of the evolutionary dynamics of quantitative traits in which the rate of change of the mean trait value is proportional to the rate of increase of individual fitness with trait value. Traits that increase ability in the predatory interaction are assumed to have negative effects on another component of fitness. We concentrate on the role of equilibrial fitness minima in producing cycles. In this case, the mean trait of a rapidly evolving species minimizes its fitness and it is chased around this equilibrium by adaptive evolution in the other species. Such cases appear to be most likely if the capture rate of prey by predators is maximal when predator and prey phenotypes match each other. They are possible, but less likely when traits in each species determine a one-dimensional axis of ability related to the interaction. Population dynamics often increase the range of parameter values for which cycles occur, relative to purely evolutionary models, although strong prey self-regulation may stabilize an evolutionarily unstable subsystem.     

生物多样性与生态系统功能:进展与争论

生物多样性与生态系统功能的关系已成为当前人类社会面临的一个重大科学问题,生物多样性的空前丧失,促使人们开展了大量研究工作来描述物种多样性-生态系统功能关系,并试图揭示多样性与系统功能关系的内在机制,本文将多样性对生态系统功能作用机制的有关假说分为统计学与生物学两大类：前者是从统计学角度来解释观察到的多样性-系统功能模式,包括抽样效应,统计均衡效应等;而后者是基于多样性的生物学效应给出的,包括生态位互补,种间正相互作用,保险效应等,本文较为详细地介绍了该领域内有代表性的实验工作,包括“生态箱”实验,Cedar Creek草地多样性实验,微宇宙实验,欧洲草地实验,以及在这些实验结果解释上的激烈争论。     

生物多样性与生态系统多功能性: 进展与展望

全球变化和人类活动引起的生物多样性丧失将会对生态系统功能产生诸多不利影响, 如生产力下降、养分循环失衡等。因此, 始于20世纪90年代的生物多样性与生态系统功能(biodiversity and ecosystem functioning, BEF)研究一直是生态学界关注的热点。然而, 随着研究的深入, 人们逐步认识到生态系统并非仅仅提供单个生态系统功能, 而是能同时提供多个功能, 这一特性被称之为“生态系统多功能性” (ecosystem multifunctionality, EMF)。尽管有此认识, 但直到2007年, 研究者才开始定量描述生物多样性与生态系统多功能性(biodiversity and ecosystem multifunctionality, BEMF)的关系。目前, BEMF研究已成为生态学研究的一个重要议题, 但仍存在很多问题和争议, 如缺少公认的多功能性测度标准、生态系统不同功能之间的权衡问题等。本文概述了BEMF研究的发展历程、常用的量化方法、EMF的维持机制和不同研究视角下BEMF的关系。针对现有研究中的不足, 本文还总结了需要进一步深入研究的地方, 特别强调了优化EMF测度方法和研究不同维度生物多样性与EMF间关系的重要性, 以期对未来的BEMF研究有所帮助。     

Biodiversity and multifunctionality in a microbial community: a novel theoretical approach to quantify functional redundancy

Ecosystems have a limited buffering capacity of multiple ecosystem functions against biodiversity loss (i.e. low multifunctional redundancy). We developed a novel theoretical approach to evaluate multifunctional redundancy in a microbial community using the microbial genome database (MBGD) for comparative analysis. In order to fully implement functional information, we defined orthologue richness in a community, each of which is a functionally conservative evolutionary unit in genomes, as an index of community multifunctionality (MF). We constructed a graph of expected orthologue richness in a community (MF) as a function of species richness (SR), fit the power function to SR (i.e. MF = cSR^a), and interpreted the higher exponent a as the lower multifunctional redundancy. Through a microcosm experiment, we confirmed that MF defined by orthologue richness could predict the actual multiple functions. We simulated random and non-random community assemblages using full genomic data of 478 prokaryotic species in the MBGD, and determined that the exponent in microbial communities ranged from 0.55 to 0.75. This exponent range provided a quantitative estimate that a 6.6–8.9% loss limit in SR occurred in a microbial community for an MF reduction no greater than 5%, suggesting a non-negligible initial loss effect of microbial diversity on MF.     

Rapid decay of diversity-productivity relationships after invasion of experimental plant communities

So far, effects of species richness on ecosystem functioning have mainly been investigated in the short term in experimental communities from which invasion was prevented. We kept the local species pools of experimental grassland communities with 1, 2, 4, 8, and 32 species closed for five years and subsequently opened them for invasion by cessation of weeding. As long as communities were weeded, extinctions were rare but positively related to species richness, diversity-productivity relationships were positive, and more diverse systems had a greater temporal stability. Following cessation of weeding, species-poor communities were more prone to invasion. However, invasion increased extinction especially in species-rich communities. Within two years, differences in species richness and biomass production between sets of communities of different initial species richness disappeared and the positive diversity-productivity relationship was no longer detectable whereas species compositions remained distinct. This indicates that the positive diversity-productivity relationships during the weeding phase were mainly controlled by species richness.Bis anhin wurden die Effekte der Artenvielfalt auf das Funktionieren von Ökosystemen vor allem in kurzfristigen Experimenten untersucht, in denen die Einwanderung von Pflanzenarten in die bestehenden Gesellschaften verhindert wurde. Im vorliegenden Versuch wurden die lokalen Artenpools von 1, 2, 4, 8 und 32 Arten unserer experimentellen Graslandgesellschaften während 5 Jahren künstlich geschlossen gehalten und danach geöffnet indem nicht mehr gejätet wurde. Solange die Gesellschaften gejätet wurden, gab es wenige Aussterbeereignisse, die aber positiv mit der Artenvielfalt korreliert waren. Die Beziehung zwischen Diversität und Produktivität war positiv und Systeme höherer Diversität zeigten eine größere zeitliche Stabilität. Nach der Aufgabe des Jätens nahm die Einwanderung vor allem in artenarmen Gesellschaften zu. Die Einwanderung erhöhte jedoch besonders das Aussterben in ursprünglich artenreichen Gesellschaften. Innerhalb von zwei Jahren verschwanden die Unterschiede in der Artenzahl und Biomasseproduktion zwischen den verschiedenen Graslandgesellschaften und eine positive Beziehung zwischen Diversität und Produktivität war nicht mehr feststellbar. Die Artenzusammensetzung der Versuchsflächen blieb jedoch unterschiedlich. Das deutet darauf hin, daß die positive Beziehung zwischen Diversität und Produktivität während der ersten Phase des Experiments vor allem durch die Artenzahl und nicht durch die Artenzusammensetzung hervorgerufen wurde.     

紫胶林-农田复合生态系统地表甲虫多样性——以云南绿春为例

为揭示紫胶林-农田复合生态系统地表甲虫多样性, 于2006-2007年在云南省绿春县牛孔乡采用陷阱法调查了天然紫胶林、人工紫胶林和旱地的地表甲虫群落。共采集标本1 678头, 分别隶属于24科120种, 其中步甲科(Carabidae)和金龟科(Scarabaeidae)种类最丰富, 均占全部种类的12.50%。拟步甲科(Tenebrionidae)个体数量最丰富, 占个体总数的64.48%; 金龟科次之, 占个体总数的17.58%。大多数科的物种数和个体数在不同土地利用生境中的分布没有显著差异, 而步甲科、隐翅甲科(Staphylinidae)、叩甲科(Elateridae)、拟步甲科、瓢虫科(Coccinellidae)和小蠧科(Scolytidae)在不同土地利用生境中的分布有显著差异。天然紫胶林地表甲虫个体数量最少, 物种较丰富, 优势度最低, 多样性最高; 人工紫胶林个体数和物种数均丰富, 优势度和多样性居中; 旱地个体数量最多, 物种最贫乏, 优势度最高, 多样性最低。种级水平的聚类分析体现出人工紫胶林与旱地之间在种类组成上距离较近; 而科级水平的聚类反映出人工紫胶林和天然紫胶林更接近。结果提示, 紫胶林-农田复合生态系统具有区域内土地利用方式多样化的特点; 天然紫胶林在维持地表甲虫多样性水平上具有重要作用, 而人工紫胶林虽具有积极作用, 但仍需进一步恢复。     

高寒草甸植物群落中相似性、物种多样性与地上生物量的年际变异性

相似性似说通过物种构成的相似性来解释物种丧失是如何影响生物量的变异性的,但还没有得到检验。本研究通过设置在青藏高原东部地区的高寒草甸植物群落中的74个永久样方．采集3年(1999～2001)植物生长高峰期的群落数据,试图检验物种构成的相似性是如何解释物种多样性对地上生物量年际变异性的影响。结果表明：随着物种丰富度增加,生物量变异性降低;而随着均匀度的增加,生物量的变异性尽管在均匀度中等程度时似乎保持在同一水平,但总体上呈下降趋势;物种构成上的相似性解释了地上生物量变异性的大部分,而且随着物种构成上的相似性的增加,生物量的变异性降低;物种丰富度和均匀度均与物种构成上的相似性没有显著相关关系。这些结果表明：尽管生物多样性的丧失可能不必导致物种丰富群落中物种构成上的相似性,但相似性与地上生物量的变异性的因果联系可能是稳健的．由于本研究是在自然群落中进行的,对物种构成的相似性没有进行直接控制,因此,要深入理解相似性是如何影响生物多样性对生态系统功能变异性的效应的机制,可能还需要直接对物种构成的相似性进行控制的实验研究。     

Declines in littoral species richness across both spatial and temporal nutrient gradients: a palaeolimnological study of two taxonomic groups

1. Using a palaeolimnological approach in shallow lakes, we quantified the species richness responses of diatoms and Cladocera to phosphorus enrichment. We also examined differences in species richness responses between littoral and pelagic assemblages of our focal communities. To address both spatial and temporal relationships, our study includes an analysis of both surface sediments from 40 lakes and of a lake sediment record spanning c. 120 years. The objective of our study was to determine whether similar species richness patterns occurred across trophic levels, as well as along spatial and temporal gradients. 2. We found that both diatom and Cladocera species richness estimates significantly declined with increasing phosphorus across space and through time. When the assemblages were subdivided according to known habitat preferences, littoral biodiversity maintained a negative trend, whereas pelagic species richness tended to show no relationship with phosphorus. 3. Negative productivity–diversity patterns have been observed across almost all palaeolimnological studies that span large productivity gradients. This congruence in patterns is most likely due to the similarity in data collection methods and in focal communities studied. The contrasting responses between littoral and pelagic assemblages may be explained by the differences in physical habitat and the pool of taxa in each of these environments. Consistent with the literature, we found statistical support for the idea that littoral diversity declines could be explained by an interaction between macrophytes and nutrients along strong trophic gradients. The general lack of a diversity response in our pelagic assemblages could be attributable to the limited pool of subfossil taxa. The response of the pelagic diatom could also be related to their broad range of nutrient tolerances. 4. The observed negative response of species richness to phosphorus enrichment, particularly in the littoral assemblages, has implications for ecosystems functioning because communities with reduced biodiversity often are less resilient to anthropogenic change.     

Mycorrhizal fungal identity and richness determine the diversity and productivity of a tallgrass prairie system

We investigated the effects of arbuscular mycorrhizal fungal (AMF) species richness and composition on plant community productivity and diversity, and whether AMF mediate plant species coexistence by promoting niche differentiation in phosphorus use. Our experiment manipulated AMF species richness and identity across a range of P conditions in tallgrass prairie mesocosms. We showed that increasing AMF richness promoted plant diversity and productivity, but that this AMF richness effect was small relative to the effects of individual AMF species. We found little support for AMF-facilitated complementarity in P use. Rather, the AMF richness effect appeared to be caused by the inclusion of particular diversity- and productivity-promoting AMF (a sampling effect). Furthermore, the identity of the diversity-promoting fungi changed with P environment, as did the relationship between the diversity-promoting and productivity-promoting benefits of AMF. Our results suggest that plant diversity and productivity are more responsive to AMF identity than to AMF diversity per se, and that AMF identity and P environment can interact in complex ways to alter community-level properties.     

Exploitation ecosystems in heterogeneous habitat complexes II: Impact of small-scale heterogeneity on predator-prey dynamics

Summary The model of exploitation ecosystems was re-analysed, assuming that habitat patches are so small that they form only parts of the home range of an individual predator. For habitat complexes where productive patches abound, the results suggested that predation will strongly spill over from productive patches, which set the tune for population dynamics within the whole landscape, to barren ones. This result conforms to the one obtained by T. Oksanen by assuming despotic habitat choice and essentially larger patch sizes. For habitat complexes heavily dominated by the barren habitat, spillover predation was predicted to be weak, as was the case in her large patch model. Unlike in her analysis, however, predation pressure was substantially reduced also within the productive habitat. In habitat complexes where patches are so small that they are exploited in a fine-grained manner, predation pressure was always found to be more intense in the barren habitat, contrary to the predictions of the original model of exploitation ecosystems. This analysis thus suggests that their model is applicable mainly on the landscape level. On the level of individual habitats, the applicability of their results depends on the habitat configuration (at its best for the prevailing habitat of the landscape and for moderate-sized patches of an essentially more productive habitat) and generally decreases with decreasing patch sizes.     

Biodiversity in microbial communities: system scale patterns and mechanisms

The relationship between anthropogenic impact and the maintenance of biodiversity is a fundamental question in ecology. The emphasis on the organizational level of biodiversity responsible for ecosystem processes is shifting from a species-centred focus to include genotypic diversity. The relationship between biodiversity measures at these two scales remains largely unknown. By stratifying anthropogenic effects between scales of biodiversity of bacterial communities, we show a statistically significant difference in diversity based on taxonomic scale. Communities with intermediate species richness show high genotypic diversity while speciose and species-poor communities do not. We propose that in species-poor communities, generally comprising stable yet harsh conditions, physiological tolerance and competitive trade-offs limit both the number of species that occur and the loss of genotypes due to decreases in already constrained fitness. In species-rich communities, natural environmental conditions result in well-defined community structure and resource partitioning. Disturbance of these communities disrupts niche space, resulting in lower genotypic diversity despite the maintenance of species diversity. Our work provides a model to inform future research about relationships between species and genotypic biodiversity based on determining the biodiversity consequences of changing environmental context.     

Predictable changes in predation mortality as a consequence of changes in food availability and predation risk

Theory predicts that animals will have lower activity levels when either the risk of predation is high or the availability of resources in the environment is high. If encounter rates with predators are proportional to activity level, then we might expect predation mortality to be affected by resource availability and predator density independent of the number of effective predators. In a factorial experiment, we tested whether predation mortality of larval wood frogs, Rana sylvatica, caused by a single larval dragonfly, Anax junius, was affected by the presence of additional caged predators and elevated resource levels. Observations were consistent with predictions. The survival rate of the tadpoles increased when additional caged predators were present and when additional resources were provided. There was no significant interaction term between predator density and food concentration. Lower predation rates at higher predator density is a form of interference competition. Reduced activity of prey at higher predator density is a potential general mechanism for this widespread phenomenon. Higher predation rates at low food levels provides an indirect mechanism for density-dependent predation. When resources are depressed by elevated consumer densities, then the higher activity levels associated with low resource levels can lead to a positive association between consumer density and consumer mortality due to predation. These linkages between variation in behaviour and density-dependent processes argue that variation in behaviour may contribute to the dynamics of the populations. Because the capture rate of predators depends on the resources available to prey, the results also argue that models of food-web dynamics will have to incorporate adaptive variation in behaviour to make accurate predictions.     

Distribution and community structure of Ostracoda (Crustacea) in shallow waterbodies of southern Kenya

The current study presents the ostracod communities recovered from 26 shallow waterbodies in southern Kenya, combined with an ecological assessment of habitat characteristics. A total of 37 waterbodies were sampled in 2001 and 2003, ranging from small ephemeral pools to large permanent lakes along broad gradients in altitude (700–2 800 m) and salinity (37–67 200 µS cm^?1). Between 0 and 12 species were recorded per site. Lack of ostracods was associated with either hypersaline waters, or the presence of fish in fresh waters. Three of the 32 recovered ostracod taxa, Physocypria sp., Sarscypridopsis cf. elizabethae and Oncocypris mulleri, combined a wide distribution with frequent local dominance. Canonical correspondence analysis on species–environment relationships indicated that littoral vegetation, altitude, surface water temperature and pH best explain the variation in ostracod communities. Presence of fish and water depth also influence species occurrence, with the larger species being more common in shallow waterbodies lacking fish. Based on Chao’s estimator of total regional species richness, this survey recovered about two-thirds (60–68%) of the regional ostracod species pool. Scanning electron micrographs (SEM) of the valve morphology of 14 ostracod taxa are provided, in order to facilitate their application in biodiversity and water-quality assessments and in palaeoenvironmental reconstruction.     

Detecting predation and scavenging by DNA gut-content analysis: a case study using a soil insect predator-prey system

White grubs (larvae of Coleoptera: Scarabaeidae) are abundant in below-ground systems and can cause considerable damage to a wide variety of crops by feeding on roots. White grub populations may be controlled by natural enemies, but the predator guild of the European species is barely known. Trophic interactions within soil food webs are difficult to study with conventional methods. Therefore, a polymerase chain reaction (PCR)-based approach was developed to investigate, for the first time, a soil insect predator-prey system. Can, however, highly sensitive detection methods identify carrion prey in predators, as has been shown for fresh prey? Fresh Melolontha melolontha (L.) larvae and 1- to 9-day-old carcasses were presented to Poecilus versicolor Sturm larvae. Mitochondrial cytochrome oxidase subunit I fragments of the prey, 175, 327 and 387 bp long, were detectable in 50% of the predators 32 h after feeding. Detectability decreased to 18% when a 585 bp sequence was amplified. Meal size and digestion capacity of individual predators had no influence on prey detection. Although prey consumption was negatively correlated with cadaver age, carrion prey could be detected by PCR as efficiently as fresh prey irrespective of carrion age. This is the first proof that PCR-based techniques are highly efficient and sensitive, both in fresh and carrion prey detection. Thus, if active predation has to be distinguished from scavenging, then additional approaches are needed to interpret the picture of prey choice derived by highly sensitive detection methods.     

The relationship between species richness and productivity in four typical grasslands of northern China

The relationship between plant species richness and primary productivity has long been a central topic in biodiversity research. In this paper, we examine the relationship between species richness and productivity in four typical grasslands of Northern China at different spatial scales. At the community scale, a positive correlation was found for six of seven communities. A unimodal pattern was found only for one community (Stipa glareosa community), while at a large scale (vegetation type or landscape/region), the relationship was also found significantly positive. Species richness ranged from 4 to 35 species, and community aboveground productivity from 13 to 368 g·m⁻²·a⁻¹. The highest species richness and aboveground productivity were found in alpine meadow, followed by meadow steppe, typical steppe and desert steppe. Translated from Biodiversity Science, 2006, 14(1): 21–28 [译自: 生物多样性]     

The relationship between species richness and productivity in four typical grasslands of northern China

The relationship between plant species richness and primary productivity has long been acentral topic in biodiversity research.In this paper,we examine the relationship between species richness and productivity in four typical grasslands of Northern China at different spatial scales.At the community scale,a positive correlation was found for six of seven communities.A unimodal pattern was found only for one community (Stipa glareosa community),while at a large scale (vegetation type or landscape/region),the relationship was also found significantly positive.Species richness ranged from 4 to 35 species,and community aboveground productiand aboveground productivity were found in alpine meadow,followed by meadow steppe,typical steppe and desert steppe.     

Impact of resource availability on species composition and diversity in freshwater nematodes

This study investigates the long-term effects of resource availability in a freshwater nematode community. We carried out a mesocosm experiment where natural nematode communities were exposed to nutrient addition/depletion over 2 years. Compared to the nutrient-addition treatment, species richness and diversity were strongly reduced upon nutrient depletion. The functional group of bacterial feeders particularly suffered severely from nutrient depletion. The decrease in diversity of bacterial feeders was linked to reduced species richness and diversity of large omnivorous species, as predicted by trophic-dynamic models. Tilmans (1976) statement, that under low nutrient levels the best competitor dominates the system, was applicable in our system. Upon nutrient depletion, resource depletion led to a monoculture of 1 small bacterial feeder, but even after 2 years of resource depletion, up to 16 species still coexisted. Our results provide strong evidence that freshwater nematode systems can be regulated by nutrient competition.